The present invention relates to a signal processing circuit and more particularly to a circuit for delaying a digital signal.
In the audio field, various systems have recently been proposed for reproducing music sounds with an affluent feeling of presence by generating a composite third sound source from conventional two-channel signals and by reproducing the third sound source at the back or lateral sides of a listener.
FIG. 1 is a block diagram of such a system for reproducing music sounds in the aforementioned manner.
A signal from a music source 10 such as a laser disk player is supplied to a main amplifier 11, and the signal is played back at front speakers SP.sub.1 and SP.sub.2.
The signal from the music source 10 is supplied also to a two-channel delay device 12 installed separately from the main system comprising the main amplifier 11 and the front speakers SP.sub.1 and SP.sub.2. The signal is delayed in the device 12 and amplified in a sub-amplifier 13 before being played back at speakers SP.sub.3 and SP.sub.4 disposed on lateral sides of the listener. The delay device 12, the sub-amplifier 13 and the speakers SP.sub.3 and SP.sub.4 form a sub-system.
In the above-mentioned system, however, since the delay device 12 of an analog type using a BBD (bucket brigade device) or the like is employed, the sub-system is by far inferior in tone quality to that of the main system in terms of the S/N ratio and the distortion factor. As a result, the feeling of presence is impaired.
Therefore, a system has recently been proposed to employ a digital delay device to improve tone quality to a greater extent. However, there is a problem that such a system needs not only an A/D converter, a D/A converter and a memory circuit but also an audio filter with high precision, as a result of which the cost of such a system becomes considerably high.